Entry of the running parameters is made on a data unit mounted in a selected position in the vehicle, as for example on the fascia panel. This data unit generally includes a plurality of manual setting elements which produce one or more parameters defining atmospheric conditions in the cabin of the vehicle.
In some cases, there are manual setting elements automatically instigate the setting up of a preferential pattern of adjustments of the installation which is pre-programmed by the manufacturer of the apparatus. In that type of installation, the user is then unable to achieve his own adjustment programmes, which means that he is obliged to define a set of parameters every time he finds himself in a particular given situation. This operation is tedious, and can be dangerous for the passengers while the driver is performing it.